1. Field of the Invention
This invention relates generally to apparatus for monitoring the voltage between a power source and a load and, more particularly, to a surge protector employing an overvoltage monitor for a power line. The invention also relates to a panelboard having an overvoltage monitor for a power line and a circuit for protecting a load from surges or transients in the power line voltage.
2. Background Information
Typically, relatively large commercial and industrial sites (e.g., electric utilities) employ equipment to monitor their power supplies or power sources. Economies of scale permit such monitoring at affordable prices. In contrast, however, small residential and light commercial locations do not monitor their source of power due to the relatively high cost of reliable voltage monitoring.
It is known to provide a power line analyzer which records or prints power line data such as, for example, short and long term voltage surges, sags, and transients. It is believed that such recorded or printed power line data, in turn, may be erased or be discarded by the user, thereby providing only temporary storage of such events.
The vast majority of damage to residential equipment is not caused by power line harmonics or blackouts, but, instead, by overvoltages. An overvoltage is an increase of steady state voltage (and, thus, power) for several cycles (e.g., at 60 Hz, 50 Hz) to several seconds. These overvoltages are caused, for example, by normal actions of the power system in clearing faults or correcting problems elsewhere in the system.
When the voltage of the power line sufficiently exceeds (e.g., as a function of both magnitude and time) its normal operating voltage, most electrical equipment is at risk of being damaged. Small surge suppression devices, which are common in most microprocessor-based equipment, are especially at risk of damage by overvoltages. For example, due to their fast response to surges and transients (e.g., a high frequency event lasting less than one power line cycle in duration), such suppression devices may, thus, react to and then be damaged by overvoltages.
Many manufacturers market surge protection devices for residential users. In this market, manufacturers have warranties to pay for damages to household equipment in the situation where the surge protection device fails to protect the residential equipment from surges or transients. However, the manufacturers"" warranties are not valid if the damage was caused by an overvoltage. Many manufacturers determine if the surge protection device was damaged. If it was damaged, then the cause is assumed to be overvoltage and the warranty does not pay for the damage. If the surge protection device was not damaged, then the warranty also does not pay for the damage.
Various known devices and arrangements protect loads from surges in power supply voltage. Generally, both series and parallel protection are employed.
There is a need for a low-cost, fast, reliable voltage monitor which can neither be reset by the end user, nor lose its memory during extended periods in the absence of power. While various devices monitor overvoltage events, no known voltage monitoring device is suitable for such use in the residential market in combination with other residential products.
This and other needs are met by the present invention in which an overvoltage monitoring circuit of a surge protector or panelboard detects an occurrence of an overvoltage event on a power line, and a recording circuit permanently records the occurrence of the overvoltage event.
As one aspect of the invention, a surge protector for electrical connection between at least one power line and at least one load comprises: an input for electrical connection to the power line; an output for electrical connection to the load; means for electrically interconnecting the output with the input and for passing power therebetween; means for protecting the load from surges or transients on the power line; means for detecting an occurrence of an overvoltage event on the power line; and means for permanently recording the occurrence of the overvoltage event.
Preferably, the means for permanently recording further includes a capacitor and a switch, with the switch being electrically connected in series with a fuse, and with the series combination of the fuse and the switch being electrically connected in parallel with the capacitor; and the means for detecting includes means for charging the capacitor from the voltage of the power line.
As another refinement, the means for permanently recording includes means for visually indicating the overvoltage event in the presence of the voltage on the power line. Also, the means for permanently recording may include means for permanently changing from a first state to a different second state, and means for permanently recording the second state independent of subsequent power fluctuations or loss of power on the power line.
As another aspect of the invention, a panelboard for electrical connection between at least one power line and at least one load comprises: at least one enclosure; an input for electrical connection to the power line; an output for electrical connection to the load; means for electrically interconnecting the output with the input and for passing power therebetween; means for protecting the load from surges or transients on the power line; means for detecting an occurrence of an overvoltage event on the power line; and means for permanently recording the occurrence of the overvoltage event.